We used to cache initializatin per-resource and check each one for
every operation. This was slower and more error prone, the
mSRGBMipmapGenerationFormat was computed every time.
Found when diagnosing crbug.com/1136613
Bug: chromium:1136613
Change-Id: Ifd804fe1dc8e26e1a9b444cc1d0c6f73954da895
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2477037Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
